SteveTrofemuk

Has anyone ever tried to build a scale zeppelin? I've been flying for around 15 years and when I first saw these airships, I thought it'd be really cool to model. At that time, the radios/servos/engines weren't small enough or light enough. Now, I think there might be a chance. Of course, the design phase would be accelerated if someone else has already done the preliminary work.

BTW, Here's a [link=http://www.lucidcafe.com/library/macon.html]link[/link] to a pretty good page describing these huge airships.

CoosBayLumber

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Blimps are more popular as they can be folded up and placed into the trunk of your auto. Peck Polymers used to offer operating blimp kits for about 20 years, and now that has passed on to another western firm.

Their Akron/Macon kits are really blimps.

Wm.

SteveTrofemuk

Thanks for the info...
I was really thinking of a rigid ship--but further searching suggests size may be a major factor. Ah well. Maybe when I build my own RC airport...

mikeceleskey

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I'm looking to do the same thing...I think it's possible. Size may be a problem..........what problem! I may have to be a trailblazer here since there doesn't seem to be much out there that anyone is doing. Considering a custom made gas bag with a rigid frame around it. Any thoughts?

fledermaus

One big problem is the fact that lighter-than-air gases (hydrogen or helium) are very small molecules (or atoms in the case of helium) and there is no fabric material that is truly impermeable to these. Recall that your helium-filled balloon always got flabby within a fairly short time. Thus, your airship will leak. Nothing you can do about it. The process is called "effusion".

Now, I don't mean to imply that the airship will deflate and fall out of the sky - it won't leak that fast - but have you looked into the cost of helium? How much helium can you afford to blow off?

The other thing is, once you fill your airship, you really can't take the helium out and put it back into the storage tank. So, unless you can transport your airship in a filled state, you will consume a full charge of helium every day you go flying. And, as I already said, you can't easily keep helium in your airship for any length of time.

So, "how did they do it in the old days?" you ask? Well, there is a reason they used hydrogen. First of all, it does actually support more weight per unit volume than helium does, but more to the point, you can MAKE hydrogen gas from simple chemical reactions (for example, pour hydrochloric acid on iron filings), and that's what they did. Airship bases had huge hydrogen generators, and they topped up the airships fairly frequently.

mikeceleskey

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how about 3 or 4 separate bags within separate frames that can be assembled/disassembled for ease of transport. Also, is there some sort of law against using hydrogen because of its instability?

fledermaus

I do not know of any "law" against the use of hydrogen - indeed, many high-altitude weather balloons are still filled with hydrogen. It is, however, a hazardous operation to handle large amounts of hydrogen gas in the presence of internal combustion engines and electric sparks.

Full-scale airships had their gas in numerous separate bladders, and there is no reason why a model couldn't do likewise. It would not actually help with the leakage problem though.

Something that I neglected to mention in my previous posting is that effusion will be a far bigger problem in a small airship than in a large one. The reason for this is that the net rate of effusion will be proportional to the surface area of the gas bladder, but the ratio of surface area to volume decreases as the size increases. That means that a small gas bladder will lose a greater proportion of its volume per unit time than a larger one will. (NB area scales as the square of the radius while volume scales as the cube of the radius - even for non-spherical shapes the proportionality is approximately the same - this means that the ratio surface/volume scales as 1/radius - it gets smaller as the object gets bigger).

So, your bags of gas will go flabby rather quickly. It is just one of those things - small atoms and molecules penetrate any material very easily and there is nothing you can do to prevent it. A helium atom or a dihydrogen molecule is about as small as things get, and the gaps between the polymer chains in any rubber or plastic are on the same size scale as these objects, or bigger. So the gases just mosey on through the material.

timothy thompson

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sounds like you know chemistry! diatomic hydrogen electron configuration1s1

mikeceleskey

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Thanks for the great input! Here is my update on "the project".....I have decided to go with 1/72 scale, so any dirigible of the '20's or '30's will be quite large. For example, the Hindenberg will be over 11' long!!!!! I have located someone in my area who can laser-cut parts for me. I could use suggestions on the lightest/strongest materials for framing as well as information on the amounts of helium it will take to lift a given weight.
I have also located several static balsa kits in various scales that are suitable for "up-scaling",specifically the "Los Angeles" and the "Hindenberg".
Thanks again,
Mike

badger41

my thoughts on this project are making bag containers to insert weather baloon ie the part that actually holds the helium, breaking the zepp into 2 or three sections and simply plug the sections together to create the full machine. this also makes it less stressfull on these bags.
The airframe could be built from carbon fiber rod, kevlar cord and carbon sheet ply and the radio gear stays in one section and connected to batteries and esc's and servos.
Each section would have it's own ballast so that assembly/disassembly is easy to handle so when fully assembled minor changes are all that is needed.
This all comes back to the year that I was involved in a minor league hockey team's r/c blimp and the trials and tribulations of meeting the schedule of a game appearence and keeping the sponsers happy since we had advertising on the craft that was changed from game to game and not always weighting the same.
We also did not have the Li-poly batteries that would have given us much more lift capability.
Also we had a good radio in haveing all that mixing capability. 8 ch Airtronics.
A lightweight fabric nylon,rayon or dacron in the finish color would help in keeping down the overall weight down. the rayon and dacron can be heat shrunk to aid in the finish process.
just some thoughts that might help.
tom

mikeceleskey

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Thanks Tom, I appreciate the input. You have been reading my mind!!!!
Mike

fledermaus

The question of how much helium is needed to provide adequate lift is pretty simple to answer: it is a buoyancy problem, similar to calculating the displacement of a ship hull in water. The lift capacity is equal to the weight of the air displaced by the airship.

An airship or balloon will float in air provided that its effective density is less than or equal to that of the air. So, first you need to know the ready-to-fly weight of your airship. The next thing you need is the density of air at your flying field under typical flying conditions, and also the density of helium at the same temperature and at the pressure you intend to fill your gas bladders to. You do NOT want to have a high pressure, by the way - the point is to have as little matter occupying as much space as possible.

In round figures, the density of dry air is about 1.25 kg m-3. You can use a more complex calculation to get the density under any set of temperatures, pressures and relative humidities if you want to - check the web for details. I found 4,950,000 hits on the phrase "density of air" from Google.

The density of helium at 20 degrees celsius (68 F) and 1 atmosphere pressure is 0.0001787 g/cm3 or 0.1787 kg m-3. Note that this is roughly 15% of the density of the air.

So, if your entire airship (including the helium in it) weighs 10 lbs (a guess that seems reasonable for the size under discussion), first of all you need to know what volume your airship must be. 10 lbs is about 4.5 kg. 4.5 kg of air occupies about 3.6 m3, so this is the minimum volume of your airship. Replacing this volume with helium requires 0.643 kg of helium, assuming that you inflate to 1 atmosphere pressure - probably you would actually inflate to just slightly more than 1 atmosphere so you might use a bit more helium.

A good sample calculation is found at [link=http://quest.nasa.gov/aero/planetary/teachers/weigh.html]http://quest.nasa.gov/aero/planetary/teachers/weigh.html[/link]


And, yes, as someone commented, I am a chemistry guy - In my "other" life I am a chem professor, although this sort of thing is a little outside my day-to-day line.

mikeceleskey

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Technically speaking.....YOU ROCK!!!!!!!!!! That is to say.....Thank You so much. I am not a "chemistry guy" in ANY life, but I love to build scale models. It just goes to show that "chemistry guys" are a valuable asset. Thanks again for your input.
Happy Easter EVERYONE!!!!!!
Mike

bmustang

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RC Modeler magazine had an article about some modelers who did build and fly a model dirigible. This had to have been in the late 1960's or early 1970's. Sorry I can't give the exact issue, but my memory isn't what it used to be. (It probably never was!)

It was not a scale model - it was pretty big and it was transparent and it was definitely a calm weather flyer!

Maybe this post will jog someone else's memory who has a better organized collection of model magazines and can tell us what issue. Even if found, I don't know how much useful information it would have for you, other than the fact that it has been done, therefore it must be possible!

Fledermaus' posts above probably have a lot more valuable technical info than the old article anyway.

I hope we see yours in a magazine someday - best of luck with the project!

Tom

mikeceleskey

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Thanks Tom for the encouragement!!!!!
How about it...anyone know of this article?
Happy Easter,
Mike

Gremlin Castle

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We have a fellow here in our club that flies and sells large non ridgid airships. His average 20 to 25 feet in length an use twin vectored thrust, self starting gas engines ranging from 38 to 55 cc. The airbags are one piece and use helium. He transports them inflated in a closed trailer and tops them off as the temperature requires. Their primary use is for advertising at large professional sporting events.

It would seem logical that a rigid airship appearing profile could be generated without a great deal of effort. Past the technical problems, probably flying it without the benefit of thrust vectoring would be the biggest problem unless you are considering semiscale flight surfaces.

aaileron

yo, new to the forum. The last reply was long ago. I wonder if anyone still checks in here. Would a rigid structure, and an envelope that is airtight , keep helium in it by simply keeping heavier gasses out?? Would helium effuse enough to cause a vaccume that would crush the airship or could the slightest negative pressure retain helium? this is not how the big ships work i realize but would it work? small scale experiment could cough up some results. If anyone allready has the goods on this i'd appreciate the help.